The present invention relates generally to improved digital data storage means, and more particularly to improved means and methods for providing write precompensation in a magnetic data storage system.
As is well known, disk drives are an important part of most modern day computer systems and there is a continuing effort to increase the storage density and reliability of such disk drives at minimum cost. As is also well known, a major problem with magnetic disk drives arises as a result of the "bit shift" occurring because of the crowding of flux reversals at high densities. Bit shift is also affected by the encoding pattern being recorded as well as by electrical and mechanical noise. During detection of the magnetically stored data, the presence of bit shift causes a bit to be detected at a time shifted by a certain amount from the expected time of detection, which, if sufficiently large compared to the bit-cell time, can cause data errors.
Known approaches for overcoming the bit shift problem (for example, see U.S. Pat. Nos. 4,245,263, 4,481,549 and 4,607,295) involve the use of what is commonly referred to as "write precompensation" which attempts to eliminate bit shift by employing predetermined precompensation of the digital data prior to its being written on the magnetic medium. These known write precompensation approaches rely on head/media performing in accordance with relatively narrow specifications. This can cause a severe yield problem during manufacture, particularly for high density systems where tolerances are tight. In addition, this reliance on narrow head/media performance specifications can increase the likelihood of uncorrectable failure, since relatively small changes in head/media characteristics after installation can defeat the write precompensation provided.